Cummins 6BT Loses it's prime

My port Cummins 6BT loses it's prime....any suggestions...thanks

Find and fix the air leak.

RickB gave the short answer. Now the question becomes where is the most likely place for the leak to be. I think I'd start with the fuel filter. It's got gaskets and o-rings that can leak and it's often opened to change the filter. The rest of the fuel system rarely gets messed with.

Yes you have an air leak. I would start with the Racor style filters as already suggested. If that doesn't solve the problem then you need to touch every connection you can find with a wrench to make sure it is tight. Make sure any clamps are tight.

No sense in talking steps after that until you do the above.

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-- Edited by jleonard on Saturday 24th of December 2011 10:00:48 AM

What fuel system maintenance was performed in the days or weeks prior to the engine losing prime?

I thought it was the fuel pump, so I installed a new one and it wotked well for about 30 hrs, now the same problem.

candyannwilliams wrote:
I thought it was the fuel pump, so I installed a new one ...

Click to expand...

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Boat maintenance advice:

Don't throw parts at a problem. That requires trips to the parts store and getting dirty changing them. It is easier to just throw the money over the side.

Test the parts you suspect before buying new ones. Unless you need a spare, your time and money is probably better utilized elsewhere.

Before you pick up a tool, pick up a pencil and paper. Write down the symptoms of the problem. Write down recent repairs or incidents even though you think they may not be related.

Read what you wrote.

Read the manufacturer's operator's or maintenance manual with particular attention to the troubleshooting section.

Approach the problem from one direction and stick to it until you have excluded the usual suspects.

Now, with that in mind, you say the engine is "losing its prime" does that mean it starts for a moment then stops because there is no fuel in the filters?

What kind of engine is it? Gas? Diesel?

How old is the engine? How many hours?

Is this a recent problem?

Did this suddenly happen or were there isolated occurrences over some period before it became a problem?

Does it just not start at all?

Do you have to bleed the injectors to start the engine after it has sat unused for some length of time?

How long does the engine have to sit before this problem shows up?

How do you restore the "prime?"

Are there any fuel weeps showing anywhere on the engine or fuel lines?

Does this happen if you shut off the tank valves after use?*

Rick, thanks for your quick response and help....here are the answers to your above questions:
The engine is a Cummins 6BT5.9 Diesel-1988 model
It only has 700(give or take) hours
It is a recent problem and there haven't been isolated occastions of it happening before
It doesn't start at all.
The enjectors or bled to start if unused for a time
20-30 minutes
The prime is restored by bleeding the injectors.
The fuel lines have been gone over and there isn't any sign of weeping
The fuel tanks are below the engines.

Again Rick Thanks for your help.

H'mmm

There is a little "bleed screw" on the center of the banjo fitting that comes out of the fuel filter. If you open that and crank does fuel immediately squirt out or does it take a while?

If you had that banjo fitting off, did you replace the copper crush washers with new or anneal them?

Are you absolutely positive that there is no weeping of fuel on any of the lines or connections when the engine is running?

also make sure that the return line is not loose,or letting air in it has been said that it will* drain the fuel from the engine inj.* it happened to me once

Thanks so much for the information-I'll check the banjo fittings in the morning and look back at the fuel lines (when I get her running again) Again I really do appreciate your help. Have a merry Christmas.

Thanks Jerry...I will also make sure that the return line is not loose,or letting any air in. Have a good one

Thanks Jerry...I will also make sure that the return line is not loose,or letting any air in. Have a good one

Most fuel systems have a check valve somewhere in the system.

Sounds like yours is leaking.

IF you install a fuel cut off at the tank, as the USCG required on 7pax and up boats ,

you might solve the problem , and gain a safety feature as well.

Thanks....we appreciate the tip.

Please let us know the ultimate solution.

If I understand correctly, your engine "loses prime" while standing for a short period of a few weeks (or less?) while not running.
We have a similar 6BTA5-9 (1999) with 2,500 hrs. and have never had any need to re-prime the fuel line even after 7 months of winter storage.
I would have to concur with others that there must be an air leak somewhere on the delivery side. The only other question I would ask (and am unable to answer)
is whether there could be some pressure in the return fuel line (closed/clogged valve, kinked line etc) that might somehow present as a similar problem.
As with Doc, would sure like to know the answer--- it could be my problem next!!

Chris


-- Edited by Chrisjs on Saturday 31st of December 2011 01:43:01 PM

Chrisjs wrote:
If I understand correctly, your engine "loses prime" while standing for a short period of a few weeks (or less?) while not running.
We have a similar 6BTA5-9 (1999) with 2,500 hrs. and have never had any need to re-prime the fuel line even after 7 months of winter storage.
I would have to concur with others that there must be an air leak somewhere on the delivery side. The only other question I would ask (and am unable to answer)
is whether there could be some pressure in the return fuel line (closed/clogged valve, kinked line etc) that might somehow present as a similar problem.
As with Doc, would sure like to know the answer--- it could be my problem next!!

Chris



-- Edited by Chrisjs on Saturday 31st of December 2011 01:43:01 PM

Click to expand...

*I would tend to agree with Chris on this one. The issue pretty much has to be in the delivery side, as the return side is open to atmosphere already.

You should see fuel somewhere.

Check for**fuel while the engine is running (anywhere after the lift pump), or fuel while the engine is sitting (anywhere prior to the lift pump).

The fuel has to leave the injection pump in order for the engine to loose its prime. It has to go somewhere. If there's no fuel then the problem is logically in a area that has no pressure or a vaccume*while the engine is running and no or little standing fuel (creating pressure) while the engine is at rest.

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-- Edited by ksanders on Sunday 1st of January 2012 09:40:18 AM

Thanks for your suggestions....we are still trying to track the problem down...as soon as we get it figured out-we will let you know.** (we are taking the dayt off-LOL) Have a happy new year!

I had a leak issue that I turned over to a mechanic(I would recommend you might do the same). It drove him crazy trying to find it. It turned out to be the remote Racor vacuum gauge that was nowhere near any other fuel system part. It was a strandard clear flexible tube that ran from the fuel "manifold" to the remote location(Main elec panel). He would not accept a penny of payment because he was so irritated with himself for not finding it sooner.


-- Edited by Baker on Wednesday 4th of January 2012 11:10:01 AM

Candyann:

Have you managed to resolve the priming problem yet? It would be good to get an update. I ma sure other 6BTA owners would appreciate the input.

Chris

x2

we never had to 're-prime' before....still working on the 'problem' but will let you know when he has it figured out for sure.** Thanks*

Chris....when my husband is sure it is fixed he will update....we*just received*new check-valves that he is going to put in....but the last few times we have run it*- it has kept the prime....so I will let you all know when we are sure of what 'fixed' it.* Thanks for your concern and interest.* It is frustrating when everything has run so perfectly for so many years.... *

I haven't given an update as the problem isn't 'solved' but we have a temp. fix until we find the air leak....we put a 12 volt fuel pump on and that is 'working'. When we fix the real problem we will post it here. I wanted to thank you all for the suggestions....Have a good weekend

Use the pump to pressurize from the tank onward and you will usually find the leak in seconds.